Active Matrix Organic Light Emitting Diodes, or AMOLEDs, have advantages such as low power consumption, low production cost, wide view angle and fast responding speed. Organic Light Emitting Diodes (OLEDs) are current-driven and their working principle is to combine electrons and hole to generate radiation light, i.e., to convert electric energy directly into light energy. Hence, they require stable currents for controlling light emission while displaying.
Conventionally, an OLED is driven by a Drive Thin Film Transistor (DTFT), which can be a P-type switching transistor. The DTFT has its gate connected to a data input terminal Vdata, its source connected to a constant-voltage power supply input terminal VDD, and its drain connected to the OLED. The voltage difference VGS created between VDD at the source and Vdata at the gate, such that the OLED connected to the drain the DTFT is on, with a driving current of the OLED IOLED=K(VGS−Vth)2 where Vth is a threshold voltage of the DTFT itself and K is a constant.
It can be seen from the above formula of the driving current that the driving current IOLED flowing through the OLED will be influenced by the threshold voltage Vth of the DTFT. Due to deviations in the manufacture process and aging of the equipment, the threshold voltage Vth of the DTFT may drift across respective pixel units, resulting in errors in the driving current flowing through the OLED and, in turn, a degraded display effect.